Best practice & research. Clinical anaesthesiology
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The use of near-infrared spectroscopy (NIRS) has been increasingly adopted in cardiac surgery to measure regional cerebral oxygen saturation. This method takes advantage of the fact that light in the near-infrared spectrum penetrates tissue, including bone and muscle. Sensors are placed at fixed distances from a light emitter, and algorithms subtract superficial light absorption from deep absorption to provide an index of tissue oxygenation. ⋯ Therefore, widespread, routine use of NIRS as a standard-of-care monitor cannot be recommended at present. Recent investigations have focused on the use of NIRS in subgroups that may benefit from NIRS monitoring, such as pediatric patients. Furthermore, a novel application of processed NIRS information for monitoring cerebral autoregulation and tissue oxygenation (e.g., kidneys and the gut) is promising.
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Best Pract Res Clin Anaesthesiol · Dec 2014
ReviewOesophageal Doppler cardiac output monitoring: a longstanding tool with evolving indications and applications.
Much work has been done over the years to assess cardiac output and better grasp haemodynamic profiles of patients in critical care and during major surgery. Pulmonary artery catheterization has long been considered as the standard of care, especially in critical care environments, however this dogma has been challenged over the last 10-15 years. This has led to a greater focus on alternate, lesser invasive technologies. ⋯ The science underpinning Doppler shift assessment of velocity stretches back over 100 years, whereas the clinical applicability, and specifically clinical outcomes improvement can be attributed to the last 20 years. Oesophageal Doppler monitoring (ODM), and its associated protocol-guided fluid administration, has been shown to reduce complications, length of stay, and overall healthcare cost when incorporated into perioperative fluid management algorithms. However, more recent advances in enhanced recovery after surgery programs have led to similar improvements, leading the clinician to consider the role of Oesophageal Doppler Monitor to be more focused in high-risk surgery and/or the high-risk patient.
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Best Pract Res Clin Anaesthesiol · Dec 2014
ReviewHemodynamic monitoring devices: putting it all together.
Perioperative hemodynamic optimization of the high-risk surgical patient is associated with reduced postoperative morbidity and mortality. The hemodynamic parameters to be optimized (using goal-directed algorithms) encompass preload, contractility, afterload, volume responsiveness, and end-organ perfusion. Current hemodynamic monitors facilitate multi-modal monitoring of these macro-hemodynamic targets. This review focuses on the variety of invasive, minimally invasive, and noninvasive hemodynamic monitors available to the clinician.
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It is often unclear whether or not a patient's stroke volume will increase following a fluid bolus. Volume responsiveness is defined by an increase in stroke volume following a fluid bolus. ⋯ However, lung-protective ventilation is increasingly being used to avoid the adverse outcomes of higher tidal volume ventilation, and pulse pressure and stroke volume variation do not effectively predict volume responsiveness in the setting of lung-protective ventilation without using special techniques. Dynamic preload assessment is more effective at determining whether a patient will be fluid responsive than static measures of preload, but further studies are needed to more conclusively show that outcomes are improved with this approach to fluid management.
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The photoplethysmographic (PPG) waveform, also known as the pulse oximeter waveform, is one of the most commonly displayed clinical waveforms. First described in the 1930s, the technology behind the waveform is simple. The waveform, as displayed on the modern pulse oximeter, is an amplified and highly filtered measurement of light absorption by the local tissue over time. ⋯ Research efforts are under way to analyze the PPG using improved digital signal processing methods to develop new physiologic parameters. It is hoped that when these new physiologic parameters are combined with a more modern understanding of cardiovascular physiology (functional hemodynamics) the potential utility of the PPG will be expanded. The clinical researcher's objective is the use of the PPG to guide early goal-directed therapeutic interventions (fluid, vasopressors, and inotropes), in effect to extract from the simple PPG the information and therapeutic guidance that was previously only obtainable from an arterial pressure line and the pulmonary artery catheter.